The present invention relates to a method for reducing the naphthenic acid content of crude oil and its fractions
Whole crudes with high organic acid content such as those containing naphthenic acids are corrosive to the equipment used to extract, transport and process the crude.
Efforts to minimize naphthenic acid corrosion have included a number of approaches. U.S. Pat. No. 5,182,013 refers to such recognized approaches as blending of higher naphthenic acid content oil with low naphthenic acid content oil. Additionally, a variety of attempts have been made to address the problem by using corrosion inhibitors for the metal surfaces of equipment exposed to the acids, or by neutralizing and removing the acids from the oil. Examples of these technologies include treatment of metal surfaces with corrosion inhibitors such as polysulfides (U.S. Pat. No. 5,182,013) or oil soluble reaction products of an alkynediol and a polyalkene polyamine (U.S. Pat. No. 4,647,366), or by treatment of a liquid hydrocarbon with a dilute aqueous alkaline solution, specifically dilute aqueous NaOH or KOH (U.S. Pat. No. 4,199,440). U.S. Pat No. 4,199,440 notes, however, that a problem arises with the use of aqueous solutions that contain higher concentrations of base. These solutions form emulsions with the oil, necessitating use of only dilute aqueous base solutions. U.S. Pat. No. 4,300,995 discloses the treatment of carbonous material particularly coal and its products, heavy oils, vacuum gas oil petroleum resids having acidic functionalities with a dilute quaternary base such as tetramethylammonium hydroxide in a liquid (alcohol or water).
U.S. Pat. No. 4,634,519 teaches a process for extracting naphthenic acids from petroleum distillates using a solvent system comprising liquid alkanols, water and ammonia in certain critical ratios to facilitate selective extraction and easy separation. The patent reaches away from use of the process to treat whole crudes, due to the formulation of an emulsion that prevented separation of the naphthenic acids (see Example 1A). What is needed is a process for separating not only certain crude fractions, but also whole crudes. Applicants"" invention address these needs.
The present invention provides for a method for decreasing the naphthenic acid content of refinery streams by contacting a crude oil or a petroleum distillate stream in the presence of an effective amount of water, a base selected from Group IA and IIA hydroxides and ammonium hydroxide and a phase transfer agent at an effective temperature (i.e., at which the water is liquid to 180xc2x0 C.) for a time sufficient to produce a treated petroleum feed having a decreased naphthenic acid content and an aqueous phase containing naphthenate salts, phase transfer agent and base.
Advantageously, this process facilitates the extraction of higher molecular weight naphthenic acids (in addition to lower molecular weight naphthenic acids), which otherwise would remain in the petroleum stream following extraction with caustic alone. This results in lower TAN content and reduced refinery equipment corrosion. Additionally, the presence of the phase transfer agent has been found to reduce the emulsion formation upon caustic treatment, and this leads to enhanced processibility.
The present invention may suitably comprise, consist or consist essentially of the described elements and may be practiced in the absence of an element not disclosed, for example in the absence of oxygen.